1. Field of the Invention
The present invention relates generally to an ink jet printhead assembly for ink jet printing apparatus and a method for the manufacture thereof. More particularly, the present invention relates to a piezoelectrically operable ink jet printhead assembly having two arrays of driving channels aligned with a single orifice array in which each orifice connects through a fluid channel to a single driving channel.
2. Description of the Prior Art
Ink jet printing systems use the ejection of tiny droplets of ink to produce an image. The devices produce highly reproducible and controllable droplets. Most commercially available ink jet printing systems may be classified as "continuous jet" or "drop-on-demand" systems. In continuous jet systems, droplets are continuously ejected from the printhead and either directed to or away from the paper or other substrate depending on the desired image to be produced. In drop-on-demand systems, droplets are ejected from the printhead in response to a specific command related to the image to be produced.
Drop-on-demand printing systems are based upon the production of droplets by thermal or electromechanically induced pressure waves. In one type of electromechanical printing system, a volumetric change in the fluid to be printed is induced by the application of a voltage pulse to a piezoelectric material which is directly or indirectly coupled to the fluid. This volumetric change causes pressure/velocity transients to occur in the fluid which are directed to produce a droplet that issues from an orifice in the printhead. According to such drop-on-demand printing systems voltage is applied only when a droplet is desired.
The use of piezoelectric materials in ink jet printers is well known. Most commonly, piezoelectric material is used in a piezoelectric transducer by which electric energy is converted into mechanical energy by applying an electric field across the material, thereby causing the piezoelectric material to deform. This ability to deform piezoelectric material has often been utilized in order to force the ejection of ink from the ink-carrying passages or channels of ink jet printers. Illustrative patents showing the use of piezoelectric materials in ink jet printers include U.S. Pat. Nos. 3,857,049, 4,584,590, 4,825,227, 4,536,097, 4,879,568, 4,887,100, 5,227,813, 5,235,352, 5,334,415, 5,345,256, 5,365,645, 5,373,314, 5,400,064, 5,402,162, 5,406,319, 5,414,916, 5,426,455, 5,430,470, 5,433,809, 5,435,060, 5,436,648 and 5,444,467.
In a representative configuration of a piezoelectrically actuated ink jet printhead, the ink jet printhead has, within its body portion, a single internal array of horizontally spaced, parallel ink receiving channels. The internal channels are covered at their front ends by a plate member through which a spaced series of small ink discharge orifices are formed. Each channel opens outwardly through a different one of the spaced orifices.
A spaced series of internal piezoelectric wall portions of the printhead body (typically formed from a piezoceramic material such as lead zirconate titanate "PZT") separate and laterally bound the channels along their lengths. To eject an ink droplet through a selected one of the discharge orifices, the two printhead sidewall portions that laterally bound the channel associated with the selected orifice are piezoelectrically deflected out of and then into the channel and then returned to their normal undeflected positions. The inward driven deflection of the opposite channel wall portions increases the pressure of the ink within the channel sufficiently to force a small quantity of ink, in droplet form, outwardly through the discharge orifice.
It can readily be seen that it would be highly desirable to provide an ink jet printhead, of the general type described above, in which the discharge orifice density (i.e., the number of ink discharge orifices per inch) is doubled without correspondingly doubling the size the printhead or the total number of components needed to fabricate the printhead. It is accordingly an object of the present invention to provide such an ink jet printhead.